Higher order modes (HOM) in specially designed fibers have recently shown to offer means to obtain robust light propagation in record-large effective areas (Aeff) with negligible mode-coupling or bend distortions. Such beams can be generated with greater than 99% coupling-efficiencies using in-fiber gratings. However, this conversion technique may not be suitable at an output of a high-power fiber-laser or amplifier comprising a HOM fiber because converting back to a (small-Aeff) fundamental mode of a fiber would lead to high intensities at the fiber output. This could then lead to nonlinear distortions and dielectric breakdown which is the very phenomena one would try to avoid by using HOM fibers.
In view of such phenomena, there exists a need to convert HOM beams by using different conversion techniques for high power applications.